Add python runtime specifier requirement

Signed-off-by: Ivan Kanakarakis <ivan.kanak@gmail.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/setup.cfg b/setup.cfg
index e56f26bc..9c25f6f4 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -44,6 +44,7 @@ scripts =
     tools/mdexport.py
     tools/merge_metadata.py
     tools/parse_xsd2.py
+python_requires = >=3.6, <4
 install_requires =
     cryptography >= 1.4
     defusedxml